Irish police have arrested a 29-year-old man in connection with the murder of Northern Ireland prison officer, David Black.

He was arrested in Co Leitrim at 17:00 GMT on Friday and is being questioned at Carrick-on-Shannon Garda station.

Mr Black was shot on the M1 motorway as he drove to work on Thursday.

Earlier the PSNI arrested two men, aged 31 and 44, in Lurgan, Co Armagh. One is Colin Duffy, a prominent republican. They are being questioned in Antrim.

The Crimestoppers charity has offered up to £10,000 for information leading to the conviction of those responsible for the 52-year-old's murder.

PSNI ACC Drew Harris said police were carrying out an extensive investigation into the killing.

"A key element of this investigation will be information which is provided by members of our community," he said.

"If the reward encourages some individuals to come forward, this will be of benefit to all our efforts as we work to secure convictions against Mr Black's killers."

Mr Black, from Cookstown in Co Tyrone, was driving to work when a car pulled up beside his vehicle on the motorway in Co Armagh and fired a number of shots. His car veered into a ditch and he died at the scene.

On Friday, the senior officer investigating the murder appealed for information about the movements of Mr Black's car and that of his killers.

DS Keith Agnew said they would do their "very best" to bring his killers before the courts.

"I welcome the universal condemnation there has been from right across our community in response to David's murder," he said.

"I am sure it is of comfort to his family at this difficult time.

"But condemnation, however strident, is not enough. My team of detectives need condemnation to be translated into information if our investigation is to make maximum progress."

Mr Black was driving a black Audi A4, with the registration number HHZ 1560.

Officers want to hear from anyone who saw it after 07:00 GMT on Thursday when it travelled from Cookstown, through Stewartstown and onto the Tamnamore roundabout before going onto the M1 eastbound.

DS Keith Agnew appealed for help to catch the killers

The killers were driving a dark blue Toyota Camry which had an Irish registration number, 94 D 50997. It was found burnt out in Inglewood in north Lurgan at 07:50 GMT.

Secretary of State for Northern Ireland Theresa Villiers described the murder as "cowardly and evil".

Speaking in the House of Commons on Friday she said: "The Government will do whatever we can to help the PSNI bring the perpetrators of this atrocity to justice.

"We will continue to do everything in our power to ensure the terrorists do not succeed."

The US Secretary of State Hillary Clinton also condemned the murder. In a statement on Friday night, she said it was a "cowardly act".

"The United States remains resolute in support of the people of Northern Ireland, who have condemned violence and embraced the path to peace and reconciliation," she said.

Mr Black, a father-of-two, was the first prison officer to be murdered in Northern Ireland in almost 20 years.

The Police Service of Northern Ireland (PSNI) have said they believe dissident republican paramilitaries were responsible for the attack.

He was a very experienced prison officer and had worked with the service throughout the Troubles.

He was the 30th prison worker to be murdered by paramilitaries since 1974 in Northern Ireland.

A book of condolence opened in Mr Black's home town, Cookstown, on Friday at the Burnavon Arts and Culture Centre on Burn Road.